Weight adj for AL to steel swap?

on_two_wheels · Mar 24, 2008

I know there's plenty of variables so I'll make this as concise as possible. Do any of the number translate into actual weight needed? Obviously full or empty, the steel is heavier. My current weight worked out GREAT on my last couple dives using the Catalina. I just bought a Faber LP 95 and PST LP 80, both steel. It would be great to quickly and accurately swap weights give the tank I'm using and maintain the same, or close to it, characteristics. So given the following numbers, any suggested starting point on how much to take out of the pouches....all else being equal?

Faber 95 LP steel:
WEIGHT EMPTY: 37.2 lbs
BUOYANCY FULL: -5.37 lbs
BUOYANCY EMPTY: 1.69 lbs

PST 80 LP steel:
WEIGHT EMPTY: 34.4 lbs
BUOYANCY FULL: -7 lbs
BUOYANCY EMPTY: -1 lb

Catalina 80 AL:
WEIGHT EMPTY: 31.6 lbs
BUOYANCY FULL: -1.8 lbs
BUOYANCY EMPTY: + 4 lbs

spectrum · Mar 24, 2008

The differences in EMPTY BUOYANCY tells the story. Just go by those deltas.

Pete

on_two_wheels · Mar 24, 2008

Meaning? I'm new to this. So going from the AL 80, I can lose a whopping 2 lbs for the steel 95 and 5 lbs with the steel 80?

David P · Mar 24, 2008

no, aluminum is +4, steel is -1. that is a 5 lb difference.

bogrady · Mar 24, 2008

Yup - just take the AL80 as the base weight and adjust your weights according to the difference in empty bouyancy.

If you carry 10 lbs with the AL80
Carry 10 - (4 - 1.69) for the LP 95
Carry 10 - (4 - (-1)) for the LP 80

Hank658 · Mar 24, 2008

That's what the numbers are saying to me. Besides just the straight numbers there are also trim considerations and overall size to think of. I use HP80's quite a bit because they are so small and portable in size compared to an AL80, as well as the added 5# that I get to leave on the boat. The LP95, while not so much a difference in buoyancy, can have a greater variation in capacity. If you choose to overfill, and there are those here that will advocate that and those who rail against it, you get more gas in your tank. There are places that can not fill a tank above 3000psi, so your 80 would get a short fill, but your 95 @ 3000psi, well, you get the idea.
The numbers also get more dramatic if you start diving doubles. +4 X 2 = +8 vs -5 X 2 = -10. Those are not completely accurate as the valves, manifold and bands adds some negative weight to those rigs.

Hope this helps!

on_two_wheels · Mar 24, 2008

Okay, let me clarify a bit more. I am weighted for using an AL80 right now. So from the numbers above, when I use the LP 80 (steel) I can remove 5 lbs of lead? Two lbs when using the 95? I'll be using both so I know that if I use the 95, I'll just remove a few lbs for the 80, add a few to go back.

Gombessa · Mar 24, 2008

So where did you get your numbers? IIRC, both the PST LP80 and the Faber LP95 are at least -1 empty. The Catalina S80 is +4 empty, so you can remove 5lb when using either steel tank.

cmburch · Mar 24, 2008

I remove about 6 lbs from my belt when going from Al80 (+4) to HP100 (-2). 4-(-2) = 6lb
For mine it would be 6 lbs.

For yours it would be 5lb LP80 and about 2.31lb for LP95.

David P · Mar 24, 2008

I believe its a typo on the 95, it should be 1.7 negative not positvie. so again your looking at 5lbs difference.

Weight adj for AL to steel swap?

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